I. Field of the Invention
This disclosure relates generally to apparatus and methods for determining headings in a wireless device, and more particularly to determining headings base on a combination of headings.
II. Background
Mobile devices used for navigation in a car or other vehicle sometimes use Global Navigation Satellite Systems (GNSS) positioning information in addition to accelerometer and gyroscope sensor measurements to formulate a current speed and heading. Such sensor measurements are most valuable when the mobile device “knows” how it is oriented with respect to the car. For example, the mobile device may be mounted in a cradle or other fixed structure in the car. Thus, when the mobile device experiences motion, the car is usually experiencing the same motion. On the other hand, if the mobile device is in a shirt pocket or sliding around on a seat or dashboard, then the mobile device motion and the car motion are correlated but not identical.
To determine whether a mobile device is mounted in a cradle, the cradle may have an electronic switch that is activated depending on whether the mobile device is in a mounted state. Each of these known cradles requires an extra switch on the cradle and an extra interface on the mobile device. Therefore, a means, without using extra cradle hardware, to detect whether a mobile device is mounted in a cradle is desired. Also, if a cradle provides pivoting or displacement with respect to the car, the relative relationship between the mobile device and car will change. Assuming that this relationship is permanently fixed while the mobile device is in its cradle is invalid with such pivoting cradles. Therefore, a means to detect when a mounted mobile device has been repositioned is desired.
In addition, many mobile devices provide heading information to a user for purposes of position location, navigation and routing. This heading information may be based on dead reckoning from sensor measurements and/or GNSS information. Such sensors include accelerometers and gyroscopes. Methods have long been desired to better select, weight and combine sensor measurements with GNSS information to provide a user with a more reliable and improved heading.
In addition to heading information, mobile devices include Kalman filters to predict a next GNSS position and velocity. The Kalman filter can better predicted the position and velocity with error feedback. Methods to provide an improve error feedback signal have long been desired.
Sensor calibration typically requires a mobile device to be stationary or traveling at a constant velocity. Methods to calibrate sensors, including gyroscopes, that have no such restraints are also desired.